Sensing assembly for linear servo accelerometer



D. E. CLARK April 19, 1966 SENSING ASSEMBLY FOR LINEAR SERVO ACCELEROMETER 2 Sheets$heet 1 Original Filed July 3, 1961 INVENTOR. Donald E. Clark 65/ 44 Attorneys D. E. CLARK April 19, 1966 SENSING ASSEMBLY FOR LINEAR SERVO ACCELEROMETER Original Filed July 3, 1961 2 Sheets-Sheet 2 Fig.6

Fig.7

INVENTOR. Donald E. Clark Attorneys Unitfid States Pat SENSING ASSEMBLY FUR LINEAR SERVO ACCELEROMETER- I Donald Em ClarlgLos-Altos, Calif., assignorfto Systron- Donner Corporation, Concord; .CalifL, a corporation of California 7 I I Continuation of application Ser. N0. 121,755, July 3,

1961'. This applicati'onSeptJQG, 1963, Ser. No. 311,767

-' 13 Claims (Cl; 737-517) to vibrate or become resonant at-"certain frequencies. In'

additiorn'such sensing "assemblies have been difiicult to manufacture and assemble, therefore making-them relativelycostly; There is,therefore, a need for anew and improved "sensing'assembly' for 1 linear servo accelerometers.v v

In general, it is an object 'ofthe 'present invention to provide a'sensingassembly for linearservo accelerometers ,which' isvery strong structurally.

Another object of the invention is to providea sensing assembly of the above character which can bereadily manufactured and assembled;

' Another object-of the invention is 'to provide a sensing assembly "of the above character in which the outer housing of the sensing assemblyforms a part of' the m'agnetic'path.

Another object of theinvention-is toprovide' a 'sensing assembly of'thej above character in which a cantilevered support system is provided for "the bearings.--

' Another object of ,the invention; is toprovide'a sensing assembly-ofthe abovewharaterfiuwhich the friction provided during ,"shock" and'vibrat'ion can be controlled while at the same timepermitting freedom of 'moyement of the moving" parts of the-sensing assembly.

Another object of "theinvention is to provide" asensing assemblyoftheabove character in which it is p'ossible' to provide dilierent resonantfrequencies for a the cantilevered supports so that vibra'ti'on effects can'be minimized:

Another object of the invention Y is "to provide a sensing assembly of the above character in which thecantilevered supports allow great flexibility to: provide the proper Another object of the 'invention'is'to provide a: sensing:

assembly of the::abve character in whichthe-paddle utilized. is formed of one solid piece.

'A'nother'object of theinvention is to provide. a sensing assembly of the: above character in" which'-' thepaddle is supported in such .a manner. togive great" mechanical rigidity; 1

Another'object :of the invention is to provide a sensing assembly of the above? character in which the paddle is less susceptible'ito vibration;

Additionalobjectsand features of-the invention will appear from :the following description inwhich preferred; embodiments are set forth in detail in conjunction with.

the. accompanying drawings... 1 Referringto the drawings:

FIGURE 1 is a side elevational'view of a sensing assembly for a linear accelerometer incorporating my invention. a

FIGURE 2 is a .top plan vie'w of the sensing assembly shown in FIGURE 1.

3,246,525 PatentedApr. 1-9, 1966 FIGURE 3 .is anexploded view of the sensing assembly shown in FIGURE. 1=showing the various parts.

FIGUREAzisa cross-sectional view taken along the line 4-4 of FIGURE-1 showing my sensing assembly.

FIGURE 5 is across-sectional view taken along the lin'eS -S. of FIGURE 2. a

FIGURE 6is across-sectional view taken along the line 6-6 of FIGURE 2.

FIGURE 7' is a cross-sectional view-taken along theli'ne 77 'of F-I'GURE 2.

In general; my sensing assembly--for linear servo accelerometers consists of a body which is provided with apair of cantilevered supports. A conducting planar element is 'pivotally mounted in the cantilevered supports and carries a coil. A magnetis disposed adjacent the coil and the bodyso that themagnetiepath passes'tlirou-gh a portion of the body and about the coil. I Pickoif means is disposed adjacent the planar-element and is mounted with in thebody: i

More in particular, as shown in' the drawings, my sensingassembly fora linear servo'accelerometer consists of a -cylindrical-caseor housing 11 -which is' provided with a pair -of external annular grooves 12 which are utilized forsecurin'gthe sensing assembly in an accelerometer by suitable'rneans such tasretaining rings. It is, however, apparentjif desired thesensing' assembly could be-fastened to any-suitable location with interconnecting leads-to the accelerometer.

An'end plug '13"is-'mounted in one end of "the openended cylindrical casell and'is-adapted to be secured to thecase- 11 by suitable means such asscrews 14. An' O-ring' 16 is provided between the plug and the case for establishing a fluid-tight seal between theen-d plug 13 and the casell. I

The'end plug 13 is formed in such a manner that it is providedwith a pair of spaced shoulders 17 which lie sub stantially in'the same plane; The endplug is also formed. with extensions 18 which extendinto 'the' case 11' and Which-are formed -to' provide flat shoulders-19lying in a plane atright angles to the plane of the shoulders 171' The end plugiis also' provided with-a supporting block 21 which lies between the shoulders 17."

."A :pair of bar magnets 23 and 24 aremounted upon the shoulders :17 adjacent thershoulders 19 by suitable means such'asby solder'sotha-t-they form-chords Wit-h respect: tofth-r: case 11. The magnets. are formed with straightsides and are provided with .arc'uate ends which conform totthe contour of the inner wall of the casing 11 as shown particularly in FIGURE 4'. Th'eilength of each of theqnagnets 23' and24is such that it is slightly less than the lengthofa correspending chord extending across;

the case. The magnets 23 and 24 are mounted in such a mannerthat one'pole of'each of the magnets abuts the inner wall of the casing: 11, whereas the opposite pole. is spaced 'from the innerwall' of the casing 11 to provide spacesx 28"betwee'n* the 'magnets and. the inner wall of the casing;-11.=

A split support ring 29 is mounted zwithin the casing andis fixed to thee'xtensions 18 ot the endplug'by suitable means such as screws 31: The support ring 29 is-provided' witht a 'supporting; .block- $2-intermedi'ate the ends of the split support ring which is opposite the supporting block-21 provided on the end plug 13. The. split support ring,29 is also provided withvan opening...33 between its ends .fora purposehereinafter described.

A pair of cantilevered supports aremounted on the supporting blockszl and 32. Each consists of a spring 7 spring members 34 have a generally triangular shape and are provided with a centrally located hole 37. A bearing 38 is mounted in the outer end of each of the spring members 34.

A paddle and coil assembly is pivotally mounted in the cantilevered support and consists of a pendulous paddle member 41 formed of a suitable conducting material such as aluminum which is provided with a centrally located hole 42 to reduce the weight and an open-ended slot 43 at one end of the paddle member. The paddle member is fiat and straight and lies in one plane as shown.

The paddle member 41 is pivotally supported in the bear-- ings 38 by pivot pins 46 which are fixed in holes 47 provided in the paddle member. The pivot pins 46 are fixed to the paddle in such a manner that they form an integral part of the paddle and provide a relatively rigid support for the paddle member. One end 41a of the paddle member serves as a conducting planar element for a purpose hereinafter described, whereas the other end of the paddle member serves as a support for a coil 51.

The coil 51 is formed of a number of turns of wire in such a manner that it is in the form of a pancake type coil provided with a central opening 52. The coil is formed in such a manner that it has an arcuate shape which has a radius which is slightly less than the radius of the inner surface of the casing 11 as shown particularly in FIGURE 4. The thickness of the coil is such that it it can move freely in the spaces 28 provided between the magnets and the inner wall of the casing 11. The coil 51 is secured to the paddle member 41 by a support block 53 which is mounted in the opening 52 and bonded to the coil by suitable means such as an epoxy resin. The support plate 53 is provided with openings 54 which can receive the leg-like portions 41b and 41c of the other end of the paddle member 41. The ends 41b and 41c, after they have been placed in the holes 54, are s'waged to securely lock the support plate to the paddle member. In addition, if desired, an epoxy fillet can be placed between the portions 41b and 410 and the plate member 53 to provide additional mechanical rigidity between the coil and the paddle member 41.

The other end of the case 11 is adapted to be closed by a cover 56 and is secured to the casing 11 by suitable means such as soldering or brazing. The cover 56 is supplied with a tapered recess 57. A diaphragm 58 is soldered in place over the recess 57 to provide an enclosed space 59 between the diaphragm and the recess 57 of the cover. An opening 61 is provided in the cover. The entire assembly. is normally filled with oil through the cap 62 provided in the end plug 13 for reasons well known to those skilled in the art. As the oil expands because of temperature changes, the oil can bleed through the opening 61 into the chamber 58. The small opening 61 prevents the oil from sloshing about within the easing 11.

A pair of leads 63 from the coil 51 are connected to a pair of terminals 64 mounted .in the end plug 13. It will be noted that the leads 63 are provided with a plurality of small loops 65 so that the leads will offer the least possible restraint to the movement of the paddle assembly as hereinafter described.

A pickoff coil 66 is mounted within the casing and consists of a plurality of turns of wire wound into a pancake type coil and mounted upon a block 67 of suitable insulating materials such as glass filled epoxy. The block is secured to one end of the magnet adjacent the end 41a of the paddle member 41 by suitable means such as an epoxy resin, so that the pickoif coil 66 lies in a plane substantially parallel to the plane of the end 41a of the paddle member 41. As is well known to those skilled in the art, the pickoff coil can consist of one coil or a pair of coils. If a pair of coils are utilized, the coils are normally wound concentrically. The lead-s 68 from the pickoif coil are connected to terminals 69 provided in the end plug. I

Operation and use of my sensing assembly may now be briefly described as follows: As is well known to those well skilled in the art, my sensing assembly is particuarly adapted for use in a linear servo accelerometer and in such an environment is normally connected to electronics. This electronics includes an oscillator which is connected to the pickolf coil, a detector which rectifies the output of the oscillator, and an amplifier which amplifies the output of the detector. A certain portion of the output from the output amplifier is fed back to the moving coil 51 to apply a restoring force to the paddle member 41 to return the paddle member to its midpoint position or to maintain the paddle member 41 in its midpoint position between the pair of magnets. An automatic balance is, therefore, established between the input forces provided by the coil 51 and the force of acceleration on the paddle member 41.

. The sensing assembly is normally positioned in such a manner that it can sense linear acceleration, that is; with the force of acceleration at right angles to the plane of the paddle member 41. With a change in acceleration, the planar conducting element 41a will move toward or away from the pickoif coil 66 about an axis which is coincident with the axis of the cylindrical casing 11. This causes a change in the current flow in the pickolf coil which causes a change in the output of the oscillator. This change in the output is detected and amplified, and fed back to the moving coil 51 to reduce or increase the restoring force applied by the coil 51. As pointed out previously, the conducting planar element 41a is positioned in a field provided by the two magnets 23 i and 24 so that a restoring force is applied to the conducting planar element 41a inla direction which is directly opposite to the force of the acceleration or deceleration.

The sensing assembly, as shown, is particularly useful in linear servo accelerometers because of several important features. The construction is simplified because a part of the casing 11 forms a part of the magnetic path. The magnetic lines of force from each of the magnets 23 and 24 pass through the air gap 28 to the casing 11 after which they travel around the casing to the other end of the same magnet. After the magnetic lines of force have crossed the air gap 28, they have a relatively easy metallic path to follow to the other pole of the magnet because the other pole of the magnet is in direct contact with the casing as can be seen particularly from FIGURE 4. A greaternumber of lines of magnetic force travel this path rather than through the path to the opposite pole of the other magnet because of the additional air gap 28 in the path. The use of the casing 11 as a part of the path for the magnetic lines of force greatly simplifies the construction of the device and at the same time increases the. magnetic forces available with a magnet having a predetermined strength.

The cantilevered supports provided for pivotally mounting the paddle and coil assembly have several distinct advantages. For example, it has been found that with such cantilevered supports in the form of the spring members 34, it is possible to control the preload forces which are applied at the bearings for the paddle and coil assembly within relatively close limits during the time severe shock forces or vibration are being applied to the sensing assembly. This is true because if a force is suddenly applied in a direction which is perpendicular to the planes of the spring members 34, both of the spring members will move in the direction which is opposite to the direction of the force'applied to maintain relatively constant contact pressures on the pivot pins 46 for the paddle and coil assembly. Thus, when shock forces are applied, the pivot supports actually move with the paddle and coil assembly.

It also has been found that with such cantilevered supports, it is possible to readily vary the spring stiffness of the spring members 34 so .that any desired degree of contact pressure can be applied to the pivot pins. This can be accomplished byincreasing the thickness of the spring members 34, increasing or decreasing the size of the holes 37, or changing the material used without changing the geometry. The spring stiffness of one of the spring members 34 with respect to the others can be changed in this manner so that each has a resonant frequency which is different from that of the other. This makes it possible to avoid vibration amplification or, in other words, makes it possible to minimize the vibration effects.

The paddle design is such that it has a great deal of mechanical rigidity which aids measurably in resistance to vibration. The pivot pins are mounted in machined holes provided in the paddle member and, therefore, give the effect of a straight shaft connected between the two bearings 38 mounted in the cantilevered supports. The paddle member itself is straight without any bends. It is believed that this strengthens the paddle member and tends to prevent the vibration of one portion of the paddle member with respect to another portion of the paddle member.

In addition to the above advantages, the construction shown is such that all the parts can be readily machined or fabricated with very little difiiculty. The parts can be readily assembled and adjusted.

It is apparent from the foregoing that I have provided a new and improved sensing assembly which is particularly adaptable for use in linear servo accelerometers. The construction is such that it can be made relatively compact without difficulty.

I claim:

1. In a sensing assembly for a linear servo accelerometer, a cylindrical housing, a pair of spaced cantilevered supports carried in said housing, a pendulous member pivotally mounted between and supported by said cantilevered supports in said housing, a conducting planar element affixed to one end of the pendulous member, a coil mounted on the other end of said pendulous member, a magnet mounted adjacent the coil and providing a magnetic field in which the coil is disposed, and pickotf means disposed adjacent the planar element, said pendulous member moving about a center point which is coincident with the axis of the housing, said coil being arcuate in form with the center of the are being coincident with the axis of the housing.

2. In a sensing assembly for a linear servo accelerometer, a cylindrical housing, a pendulous member pivotally mounted in said housing, a conducting planar element atfixed to one end of said member, a coil mounted on said member, a pair of magnets mounted in said housing and having one end of each of the same substantially abutting the housing and having the other end of each of the magnets spaced from the housing to form air gaps between the magnets and the housing, the magnets being spaced apart so that a substantially greater number of magnetic lines of force travel through said air gap and the housing than directly between the magnets, the coil being disposed in the air gaps and being adapted to move in the air gaps, and pickoff means disposed adjacent the planar element, the pivot axis for the pendulous member being coincident with the axis of the housing, said coil being in the form of an arc concentric with the housing.

3. A sensing assembly as in claim 2 wherein said pendulous member is carried on cantilevered supports mounted in the housing, said cantilevered supports being in the form of spring members disposed on opposite sides of the pendulous member.

4. In a sensing assembly for a linear servo accelerometer, a cylindrical casing, a pair of supporting members fixed to said casing, a pair of cantilevered spring members fixed to said support members, a paddle member pivotally mounted between and supported by said spring members so that its axis of pivot is coincident with the axis of the casing, a planar conducting element mounted on one end of said paddle member, an arcuately-shaped coil concentric withthe casing mounted on the other end of said paddle member and lying generally in a plane at right angles to the con-ducting planar element, a pair of magnets mounted in said casing in a direction generally parallel to the normal position of said paddle'member, one 'end of each of the magnets being adjacent the casing and the other end of each of the'magnets being spaced from the casing toprovide a spacebetween it and the casing in which the coilmay travel, and pickoff means disposed adjacent the planar element.

5. A sensing assembly as in claim 4 wherein said paddle member and said conducting planar element are an integral piece of conducting material lying in a single plane.

6. A sensing assembly as in claim 5 whereirrsaid paddle member is pivotally supported in said cantilevered spring members by a pair of pivot pins fixed to the paddle member and extending from the paddle member in the same plane as the paddle member.

7. A sensing assembly as in claim 4 wherein said mag nets are bar magnets and lie in planes which define chords on the cylindrical casing.

8. A sensing assembly as in claim 7 wherein said magnets are provided with arcuat-e ends which conform to the contour of the inner surface of the cylindrical casing.

9. A sensing assembly as in claim 5 wherein said cantilevered spring members are generally triangular in shape and have a centrally disposed opening therein.

10. In a sensing assembly for a linear servo accelerometer, a housing, a pair of spaced compliant cantilevered supports mounted upon said housing, said compliant cantilevered supports being substantially triangular in shape and having apex and base portions, a pendulous member pivotally mounted between the cantilevered supports at points adjacent to the apex portions of the triangular supports for movement on a pivot axis, the base portions of the cantilevered supports being rigidly secured to the housing, a conducting planar element afiixed to one end of the pendulous member, a coil mounted on said pendulous member, a magnet disposed adjacent the coil and providing a magnetic field, portions of said coil being dispose-d in the magnetic field, and pickoif means disposed adjacent the planar element.

11. In a sensing assembly for a linear servo accelerometer, a housing, a pair of spring-like members, said springlike members being substantially triangular with apex and base portions, the base portions of the spring-like members being rigidly secured to the housing so that the spring-like members are disposed in a spaced, substantially parallel relationship facing each other, a bearing mounted on each of said spring-like members adjacent the apex portion of the spring-like member, a pendulous member pivotally mounted in said bearings for pivotal movement about a pivot axis, said spring-like members forming cantilevered supports for said pendulous member, said spring-like members permitting movement of the pendulous member in a direction parallel to the pivot axis, a conducting planar element aflixed to one end of said pendulous member, a coil mounted on said pendulous member, a magnet disposed adjacent the coil and providing a magnetic field, a portion of the coil being disposed in the magnetic field, and pickoff means disposed adjacent the planar element.

12. In a sen-sing assembly for a linear servo accelerometer, a housing, a pair of planar spaced-apart spring-like members, said spring-like members being substantially triangular with base and apex portions, the base portions of the spring-like members being rigidly secured to said housing to provide cantilevered supports having apex portions which are free to move, a pendulous member, means for pivotally mounting the pendulous member between said spring-like members to permit movement of the pendulous member about a pivot axis substantially perpendicular to the planar spring-like members, said means for pivotally mounting the pendulous member consisting of bearing means mounted on the spring-like members adjacent the apex portions, and pivot pins mounted in the pendulous member and engaging said bearing means on the spring-like members, said spring-like members permitting movement of the pendulous member in a direction along the pivot axis, a conducting planar element aflixed to one end of the pendulous member, a coil mounted on said pendulous member for movement with the pcndulous member, a magnet disposed adjacent the coil and providing a magnetic field, at least a portion of the coil being disposed in the magnetic field, and pickofi means disposed adjacent the planar element.

13. A sensing assembly as in claim 12 wherein said triangular spring-like members have relatively large holes centrally positioned therein to reduce the mass of the spring-like members.

References Cited by the Examiner UNITED STATES PATENTS 2,427,529 9/1947 Hickok et a1 324-155 2,633,544 3/1953 Herr 308-159 2,734,736 2/1956 Payne 73-398 2,802,956 8/1957 Jarosh et al. 73-516 2,901,298 8/1959 Carpenter 308-159 2,985,021 5/1961 Lewis et a1. 73-517 3,074,279 1/1963 Morris 73/517 RICHARD C. QUEISSER, Primary Examiner.

JAMES J. GILL, Examiner. 

1. IN A SENSING ASSEMBLY FOR A LINEAR SERVO ACCELEROMETER, A CYLINDER HOUSING, A PAIR OF SPACED CANTILEVERED SUPPORTS CARRIED IN SAID HOUSING, A PENDULOUS MEMBER PIVOTALLY MOUNTED BETWEEN AND SUPPORTED BY SAID CANTILEVERED SUPPORTS IN SAID HOUSING, A CONDUCTING PLANAR ELEMENT AFFIXED TO ONE END OF THE PENDULOUS MEMBER, A COIL MOUNTED ON THE OTHER END OF SAID PENDULOUS MEMBER, A MAGNET MOUNTED ADJACENT THE COIL AND PROVIDING A MAG- 